In a great number of engineering fields, high-grade metallic and non-metallic components i.e., compacts are manufactured from powders. For this purpose, powder starting materials of metals and/or metalloids are subjected to treatments such as heat and pressure to convert the powder materials into compacts substantially corresponding to the final shape of the components. The treatment and shaping processes may be conducted in a single stage or in multiple stages.
The properties of the components or compacts made from powders vary mainly according to the properties of the powder. Namely:
Surface layers on the power particles affect the sintering performance and the material properties that are influenced by the particle boundary; PA1 Segregations in the powder particles affect the strength or the cracking tendency; PA1 Gaseous inclusions in the powder particles affect the gas content and porosity of the finished part. PA1 a. For ceramic materials SiC core; envelope of carbon+borium Si.sub.3 N.sub.4 core; envelope of sintering promoting material such as yttrium oxide PA1 b. For metals Deposit borium of lower melting point on powder surface to make it possible to use liquid phase sintering PA1 c. For glass (metalliferous) Add metalloids such as borium to raise the crystallization temperature.
Further properties of the components or compacts made from powders, such as the physical, electrical, chemical and thermal properties, likewise vary according to the properties of the powder, so that a compact made of spherical powder particles (prior to heat treatment, such as sintering), normally exhibits poor shape stability, which makes it difficult to handle these green compacts. Spattered or dendritic powder will normally greatly reduce the strength of the green compact.
The powder is manufactured by various methods. These include primarily spraying, liquefying or atomizing metallic materials at temperatures above the melting point. This produces spherical or spattered powder, depending on whether the metal droplets were developed before or after contact with solid surfaces.
The manufacture of powder from the vapor phase by chemical vapor deposition (CVD) or physical vapor deposition (PVD) is known for the manufacture of non-spherical powders. The manufacture of powder in a floating condition, without the particles building up on stationary surfaces, has its limitations under gravitation conditions. These are imposed by the difficulty of admitting the gas required for flotation or by the limited spatial extent of the reaction (vacuum) vessels.
One great problem in the known process is in adding sintering promoting materials into the powder. These materials should be as uniformly distributed as possible and should be used as sparingly as possible. Accumulations of sintering promoting materials can cause differences in density, distortion, local stress and ductility losses, and the like in the finished product.